Touch sensors are solid state switches that respond to a user's touch or encroachment. As such, they often can be used in place of conventional mechanical switches. Known touch sensors typically include a touch pad having one or more electrodes and an associated circuit that induces an electric field about the touch pad and responds to changes in the electric field when the electric field is disturbed by a stimulus such as a user's touch or proximity. The touch pad and associated circuit typically are disposed on a substrate such as a printed wiring board or a piece of glass. A portion of this or another related substrate typically defines an operative touch surface which the user must touch or approach to provide the stimulus required to trigger the touch sensor. The control circuit can be configured to control a device such as a light, motor or other device.
Several types of touch sensors are known in the art, including capacitive touch sensors, infrared touch sensors, electric field touch sensors, acoustic touch sensors and electromagnetic touch sensors. Such touch sensors can be configured as described in U.S. Pat. No. 5,594,222, No. 5,856,646, No. 6,310,611, and No. 6,320,282 and in many other ways.
Touch sensors can be used as part of an input/output system where some form of aural or visual feedback is provided. Feedback can involve either alerting the user to the presence of an operative touch surface or informing the user that a touch has triggered a response in the touch sensor. In many cases, visual feedback involves back-lighting the operative touch surface or other areas on an interface panel. Backlighting can be provided by a light emitting diode (LED) or a light emitting polymer (LEP), including an organic light emitting diode (OLED) or a polymer light emitting diode (PLED) (both of which are LEPs), or any other suitable light source.
LED, OLED and PLED devices convert electrical energy to light energy in the form of photons. These light emitting devices can include either a transparent anode or a transparent cathode through which the photons generated at their light emitting layers can pass. The light emitting layers of LEDs include semiconductors with doped physical lattice crystal structures. The light emitting layers of OLEDs and PLEDs are composed of small organic molecules and relatively larger organic molecules, respectively. All of the foregoing light emitting devices are typically very thin and can be constructed into point sources or can be made to illuminate large areas, but it may be more economical to do so with OLEDs and PLEDs than with semiconductor devices like LEDs. Using thermal evaporator, thin film sputtering or spin coating techniques, both OLEDs and PLEDs can be mass produced in fewer steps than can semiconductors and may also be economically produced using micro-deposition or ink jet and spin coating equipment. Light produced by any light source can also be spread out or diffused using lenses, light pipes and other suitable devices.
Because backlighting can be advantageously aligned with an operative touch surface, it is sometimes desirable to locate a touch sensor in close proximity to and/or atop a light emitting device. In the latter case, the touch sensor's electrodes preferably are transparent to allow the light produced by the light emitting device to reach the user. In the prior art, these electrodes are separate components of the backlit touch sensor. Because the touch sensor and backlighting device are separate components, the electrical addressing required to drive them both is often complicated and costly. In cases where the touch sensor must overlie the light emitting device, the light from the light emitting device can be attenuated by the transparent layers of an OLED or PLED and further by the touch sensor components before it reaches the user. In all cases, aligning a light emitting device with a separately constructed touch sensor involves extra material and other manufacturing costs owing to the required connections and alignment of the two.